The purpose of this study was to determine the effects of a dietary mushroom glucan on the non- specific immune responses and disease resistance of the Indian major carp, Catla catla. Glucan was extracted from farm-raised edible mushrooms (Pleurotus florida). The glucan was fed to test animals for two weeks at 0.5 g or 1 g/kg feed. Afterward, the fish received the control diet for another four weeks. Non-specific immune responses were measured at the end of the two-week experimental feeding (week 0), two weeks later (week 2), and four weeks later (week 4). Control and test fish were challenged by intraperitoneal injection of the fish pathogenic bacterium, Aeromonas hydrophila, seven days after the two-week experimental feeding period. Mortality was observed and the relative percent survival was calculated. In the 0.5 g treatment, significant enhancement (p<0.05) in superoxide anion production was observed at weeks 0 and 2. In the 1 g treatment, activity was enhanced only at week 2. Both concentrations significantly increased phagocytosis at weeks 0 and 2 and bactericidal activity at weeks 2 and 4 (p<0.05). Alternative complement pathway activity was unaltered by either treatment (p>0.05), but lysozyme activity was raised at weeks 2 and 4 in the 0.5 g treatment and at week 2 in the 1 g treatment. Both con- centrations significantly enhanced relative percent survival.